Update repositories.txt

[ladyada]

add https://github.com/adafruit/Adafruit_AS5600/

[github-actions]

Arduino Lint has suggestions for possible improvements to https://github.com/adafruit/Adafruit_AS5600:

Linting library in Adafruit_AS5600
INFO: No header file found matching library name (Adafruit_AS5600_Library.h). Best practices are for primary header     
      filename to match library name.                                                                                   
      See: https://arduino.github.io/arduino-cli/latest/library-specification/#libraryproperties-file-format            
      (Rule LS008)                                                                                                      
WARNING: library.properties name Adafruit AS5600 Library contains spaces. Although supported, best practices is to not  
         use spaces.                                                                                                    
         See: https://arduino.github.io/arduino-cli/latest/library-specification/#libraryproperties-file-format         
         (Rule LP015)                                                                                                   
WARNING: Library name Adafruit AS5600 Library contains "library". This is superfluous.                         
         See: https://arduino.github.io/arduino-cli/latest/library-specification/#libraryproperties-file-format
         (Rule LP016)                                                                                          
WARNING: No license file found.                                                                                                                 
         See:                                                                                                                                   
         https://docs.github.com/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/licensing-a-repository
         (Rule LD002)                                                                                                                           

Linter results for project: 0 ERRORS, 3 WARNINGS

-------------------

Linting sketch in Adafruit_AS5600/examples/AS5600_basic

Linter results for project: no errors or warnings

-------------------

Linting sketch in Adafruit_AS5600/examples/AS5600_fulltest

Linter results for project: no errors or warnings

-------------------

Linter results for projects: 0 ERRORS, 3 WARNINGS

[github-actions]

Your submission has now been accepted! Thanks for your contribution to the Arduino Library Manager index.

The library(s) will be available for installation via Library Manager within a day's time.

You can check the logs from the Library Manager indexer for your library(s) here:
http://downloads.arduino.cc/libraries/logs/github.com/adafruit/Adafruit_AS5600/